i've had many like these, both the shiny irregular agate ovals and the pebbly cornelian ones with a rubbed, matte surface, which are really beautiful.
they came from Indian dealers, not very recently. some were worked into more recent necklaces with cheapish metal beads between or used with beads that looked more "tibetan". Peter Francis said that the shiny flat cornelian tabular discs were re-cycled by-products of the small industry that cut finger rings from stones- using the middles, not throwing them out. some have a central hole.
one of my close friends wears a short necklace of those flat discs i made her years ago which occasionally needs rethreading because the holes are not too smooth or straight and any threading material, even nylon-covered steel cable eventually breaks. irregular drill-holes is often a sign of origins in India.